1. Field of Invention
The present invention relates to the field of a power-assist bicycle, and more particularly to an electric power-assist bicycle for providing a power-assist signal by performing multi-point magnetic induction on a rotating component.
2. Description of Related Arts
A Chinese patent application having an application number of CN 201020295192.0 by Yebao automotive materials Industry Co. Ltd disclosed a power assistance bicycle dedicated sensing device which is cooperated by a magnetic part and a flexible assembly and capable of sensing torque. After a long time utilization, changes of spring constants of the flexible assembly lead to changes of control effects of the sensing signal and the controlled motor, so that the control effects can not meet the requirements of people's assistance. In addition, the flexible assembly has a complicated structure and a high cost.
A Chinese patent application “automatic detection device for electric assistance bicycle” with a publication number of 01201843.0 by Beijing University of Science and Technology discloses an automatic detection device for an electric assistance bicycle. The device detects the pedal force, the speed and the steering without contacting. In the device, discs are respectively provided on an inner wheel disc and an outer wheel disc which moves relatively. A spring is provided on the inner wheel disc. The spring is provided between the inner wheel disc and the outer wheel disc for resetting. Two Hall elements on a support detect electrical signals generated by relatively moved discs on the inner wheel disc and the outer wheel disc to represent the pedal force, the speed and the steering.
Disadvantages of the devices mentioned above are as follows.
Disadvantage (1)
The flexible assembly utilized is not durable. After a time of utilization, changes of spring constant of the flexible assembly lead to control effect changes of the controlled motor, so that the control effects can not meet the requirements of people's assistance. In addition, the flexible assembly has a complicated structure and a high cost.
Disadvantage (2)
The sine wave outputted allow a disc group edge distance of not less than 4 cm, and preferably 5 cm, which causes a result that the number of the magnetic sheet groups are too few and that the man-machine cooperation is not satisfying. If each group of magnetic sheets is identical, the output of the Hall element is sine waves for serving as the control signal. The sine waves serving as the control signal must have a peak-valley difference value. Since the magnetic sheet group in the application needs a certain length for representing the forward and reverse movement. The circular path of the annular-groove rotating disk with a diameter of 20 cm has at most 8 magnetic sheet groups provided thereon, and preferably 5, in such a manner that the Hall element is capable of generating sine wave signals having control function. In other words, when the technical solution of the patent application of 01201843.0 is utilized in a power assistance bicycle, the number of the magnetic sheet groups is limited to 8, the number of the control signal is too few and the man-machine cooperation is not satisfying. However, if the magnetic sheet groups are more than 8, the signal graph outputted by the Hall element is close to a horizontal line when a man rides on the bicycle in a fast speed. The signal does not have a control function and is not capable of controlling the motor, so that when the assistance power is particularly required, the power assistance function is lost.
Disadvantage (3)
The blind zone of the signal has a blind angle of 45 degrees, and the assistance power can not be obtained when required in starting. It is well known that the torque is minimal when a man steps on the pedal vertex of a bicycle. An area 10-45 degrees away from the vertex is the area requiring the assistance power most. However, in the patent application, the included angle among each magnetic sheet group is 45 degrees. The area 10-45 degrees away from the vertex of the pedal has no magnetic sheet group, i.e., no control signal. And the result is that the motor of the power assistance bicycle is not capable of providing assistance power while requiring the assistance power most.
In summary, except that the flexible assembly is not durable and has complicated structures, the diameter of the wheel is within 20 cm, which limits the number of the magnetic sheet group to 8. Thus, the groups of the magnetic sheets can not be added optionally, the man-machine cooperation is not satisfying, the assistance power is not available while starting. The assistance power can not meet the requirements. The cyclist is not comfortable while riding. If the number of the magnetic sheet groups is added forcibly, the sensing signals thereof loose the assistance power control function.
A Chinese patent application sensor for time-like electric power bicycle having a publication number of 03264387.X by Naikang Wang discloses a sensor without a flexible assembly. The sensor comprises a rotating disc and a stationary disc. Two permanent magnets are inset in the rotating disc. Three Hall elements are inset in the stationary disc. When the pedal of the bicycle rotates one cycle, each Hall element generates two pulses, and thus three Hall elements generate six pulses. Three features and four disadvantages of the patent application by Naikang Wang are analyzed as follows.
Feature (1)
In order to obtain six pulse signals, the same magnetic poles of the two permanent magnets are provided on a same side of the rotating disc, i.e., the two poles N or the two poles S of the two permanent magnets are on a certain side of the rotating disc. If a pole N of one permanent magnet and a pole S of another permanent magnet are on a same side of the rotating disc, each Hall element is only capable of generating one pulse by rotating the pedal one circle, and the three Hall element is only capable of generating three pulses, which is not in accordance with the disclosure of the specification of the patent application. In order to increase the pulses and the control effect, the same magnet poles of each permanent magnet can only be on an identical side.
Feature (2)
The permanent magnets are for presenting stationary positions of the pedal. The three Hall elements are for presenting motion positions of the pedal. Since the pedal and the rotating disk rotate synchronously, one permanent magnet is respectively provided on two positions of the rotating disc corresponding to the two pedals. The rotating position of a pedal is the rotating position of a corresponding permanent magnet. However, only when the rotating at the position of the Hall element, can the Hall element send a control signal, by which to instruct the power assistance bicycle to generate the assistance power to rotate.
Feature (3)
Since one Hall element is not capable of representing the motion positions in one rotating circle of the pedal at different times, utilizing only one Hall element is not desirable. The pedal has a great different requirement for the assistance power at different times of the rotating circle. In order to represent the variations of requirements for the assistance power, three Hall elements are respectively provided on three positions within 180 degrees in the patent application. Two permanent magnets are respectively provided on the positions of the pedal. The pedal rotates in a position of the Hall element, and the Hall element outputs signals for representing that the pedal reaches the position of the Hall element. However, utilizing multiple Hall elements has disadvantages as follows.
The features of the sensor of the power assistance bicycle have three disadvantages as follows.
Disadvantage (1)
Two identical permanent magnets respectively represent stationary positions of the two pedals. Multiple Hall elements are utilized for representing the rotating position of the pedals. The two identical permanent magnets have advantages that the stationary positions of the two pedals can be represented respectively with no differences between the left foot and the right foot. The left foot and the right foot have requirements for the assistance power and are capable of generating the same assistance effects to the motors. The disadvantage is that the permanent magnet itself is not capable of representing the rotating position of the pedal, and the rotating position of the pedal can only be represented by the positions of the multiple Hall elements provided on different corner positions. Thus, utilizing only one Hall element is infeasible, and multiple Hall elements must be utilized.
Disadvantage (2)
As utilizing one Hall element is infeasible, utilizing three Hall elements inevitably leads to original segment errors of three control signals, which causes distortion of the required power assistance model, so that the output of the assistance power is not in accordance with the requirements of the assistance power. No matter the power assistance bicycle has one motor or two motors, the motor signals controlled thereby can only achieve the object of controlling the motor by only one controller of sensing signal inputting motor. However, in the patent application, three Hall elements are utilized for controlling the motor, so only when the three control signals of the three Hall elements are combined into an integrated control signal, the control signal can be inputted to the motor controller. Sensor parameters of the three Hall elements can't be the identical. Particularly, due to variations of the environment temperatures, the sensor parameters of the three Hall elements may have great differences, which cause a result that different Hall elements output different voltages under the same power assistance requirements. Thus, the motor generates different outputs of assistance power, and the output of the assistance power id not in accordance with the requirements for the assistance power. Similarly, when identical assistance power is required, different Hall elements may output an identical voltage, so that the motor generates only one identical assistance power to output, which also brings the problem of inconformity between the outputs and the requirements of the assistance power.
Disadvantage (3)
The integrated control signal is easy to generate a signal drift, so that the integrated control signal does not match with the motor controller and that the power assistance model is distorted. Due to variations of the environment temperatures, the sensor parameters of the three Hall elements may have great differences after utilizing for a long time, which certainly leads to variations of three control signals of the three Hall elements, so that the integrated control signal generated by an identical power assistance requirement generates a segment signal drift. Thus the integrated control signal as a whole generates the segment signal drift, i.e. the assistance power model is distorted, which causes a result that no matter the motor controller selects any one of the three control signal for serving as a reference, the problems of inconformity between the requirements and the outputs of the assistance power.
Disadvantage (4)
Sensing sites can not be added randomly. The number of the sensing sites is too few, so that the operation of the motor is unstable and the rider feels uncomfortable. Since the disadvantages (1) and (2) are caused by the fact that the number of the Hall elements is over one, the more is the number of the Hall element, the more serious is the disadvantages (1) and (2). Thus, the power assistance bicycle provided by the patent application is a power assistance bicycle that makes the rider feels uncomfortable.
Disadvantage (5)
The bind zone of the signal has a blind angle reaching 42 degrees. The assistance power is not available when required. It is well known that
The blind zone of the signal has a blind angle of 45 degrees, and the assistance power can not be obtained when required in starting. It is well known that the torque is minimal when a man steps on the pedal vertex of a bicycle. An area 10-45 degrees away from the vertex is the area requiring the assistance power most. However, in the patent application, the included angle among each magnetic sheet group is 42.5-43.5 degrees. The area 10-42 degrees away from the vertex of the pedal has no Hall elements, i.e., no control signal. And the result is that the motor of the power assistance bicycle is not capable of providing assistance power while requiring the assistance power most.
In summary, the patent application adopts a technical solution of controlling the power assistance model by multiple Hall elements. Since the rotating positions of the pedal can only be presented by multiple Hall elements, the multiple Hall elements controlled signals must have original errors; and the integrated control signal is easy to generate signal drift. Both of the situations cause distortion of the assistance power required model, i.e., the identical power assistance requirements at different times obtains different power assistance effects. The more is the number of the Hall elements, the more serious is the distortion degree of the power assistance required model, which limits the number of the Hall elements. The few amounts of the Hall elements cause a result that the operation of the motor is not steady, the rider feels uncomfortable, and that the assistance power is not available when starting. Thus, the patent application by Naikang Wang always attends to one thing and loses sight of another between the distortionless of the power assistance requirement model and the steady operation of the motor, and it is not possible to have both ways.